There are two forms of imperfect subjunctive, which are used indistinguishably. See the box to the right for instruction in the formation of the imperfect subjunctive.

One of the most common uses of the imperfect subjunctive is in a "si" (if) clause. In such a clause it has a hypothetical meaning.

Si fuera española, no le costaría nada.
If you were Spanish, it would not cost you anything.

Si fueran invitados al coctel estoy seguro de que irían.
If they were invited to the cocktail party, I'm sure they would go.

Si fuera tan rico como tú sería igual de aburrido.
If I were as rich as you I would be just as boring.

Another common use of the past subjunctive is in the same situations that you would use the present subjunctive: persuasion, doubt, or value judgement. If the verb in the main clause is in the past, the subordinate clause will use the past subjunctive.

El jefe quería que fueras a la junta.
The boss wanted you to go to the meeting.

No me parecía muy seguro que soltáramos desde ese precipicio alto.
It didn't seem very safe to me that we jump from that high cliff.

Estuvo bien que trabajaras las horas extras.
It was good that you worked the extra hours.

Me gustó que Mario viniera a la fiesta.
I liked it that Mario came to the party.

Esperaba que Juan viniera a la fiesta.
I was hoping for Juan to come to the party.

Me gustaría que Sam viniera a la fiesta.
I would like it for Sam to come to the party

The imperfect subjunctive can also be used to express a polite request or desire.

Quisiera comprar este libro.
I would like to buy this book.